With the advances of cloud computing and multimedia communication, cloud gaming has been proposed to enable rich multiplayer Internet games. In a cloud gaming platform, control and button inputs from the client are transmitted to the server. In response, the server renders and compresses the game images, and transmits them to the client display. In other words, computationally-intensive rendering and game logics are executed on the powerful cloud servers instead of client terminals.
Cloud gaming can offer several advantages. Since the games are rendered and managed on the powerful servers, users can play rich multiplayer games using low-end consoles or power-constrained mobile devices. Cloud gaming has the potential to transform any handheld device into a powerful gaming machine, enabling photo-realistic game content on mobile clients. Furthermore, as the games are stored on the servers, cloud gaming can effectively address the piracy issue and simplify distribution. In addition, the cloud gaming platform is deemed to be particularly suitable for serious games such as rehabilitation games or educational games. As game logic resides in the cloud, cloud gaming can greatly facilitate performance monitoring, customization for individual need and timely feedback, which are preferably present for serious games.
With its potential advantages, cloud gaming has attracted a lot of interests recently. For example, Sony purchased cloud gaming services from a platform provider called Gaikai in 2012 [27], and will be incorporating some cloud gaming functionalities into its game consoles [28]. Samsung has announced plans to stream games to its Smart TVs [6]. This allows users to access popular game titles without the need for game consoles. Recently, NVIDIA has also developed powerful server-side rendering boards, with a brand name GRID [19], which include massively parallel rendering engines of up to 3072 processing cores per board, and are capable of supporting up to 24 concurrent game users per board.
Despite the advantages and strong industrial interests, cloud gaming faces some of the most stringent challenges for multimedia communication. With the technology to date, first, computation-intensive rendering and game content compression need to be performed for individual users at the cloud servers in real-time. Second, high-quality, high-frame-rate graphics of immense data-size need to be streamed under stringent latency requirements. Third, existing cloud gaming requires user bandwidths as high as several gigabytes per hour data download rates. In other words, bandwidth consumption and latency are two main challenges of current cloud gaming. This prohibits widespread adoption in many regions with usage-based Internet billing. While the computation challenge may be addressed by recently-developed cost/power-efficient rendering hardware, the latency and bandwidth challenges remain highly difficult. Currently, almost all existing cloud gaming services require users to have high-bandwidth dedicated connections. Mobile cloud gaming services, which stream game contents over wireless networks, are rare.
Most existing cloud gaming platforms employ standard, off-the-shelf video codecs for game image compression, notably H.264/MPEG-4 Part 10 Advanced Video Coding (AVC) [33]. H.264 and the recently standardized High Efficiency Video Coding (HEVC)/H.265 video coding [29] rely strongly on inter-frame correlation to reduce the source bitrate. Many games (e.g., first person shooter games), however, exhibit rapid camera motion and their temporal correlation tends to be small. This affects the compression performance. In addition, high-quality games demand crisp details and pristine content quality, and these require very high transmission bit-rates with the state-of-the-art video compression technology.